FastCompany had an interesting scoop today about popular photo-sharing app company Instagram. Today, Instagram finally opened up its API to third-party apps and services, and the first app to take advantage of this is the also-popular camera app, Hipstamatic.

Instagram is a hugely successful photo-sharing service, now with 27 million active users. It’s available only for iOS devices currently, but an Android release is expected soon. Meanwhile, Hipstamatic allows iOS users to snap photos using all manner of interesting retro filters to look like the images have been created with vintage-era lenses.

Now, Hipstamatic users will be able to port their favorite shots directly to Instagram’s network instantly. Hipstamatic founder and CEO, Lucas Buick, said, “When we launched, it was all about Facebook and Flickr and Twitter, and now we're seeing a huge shift in our user base toward Instagram. We've never been a social networking company, but we clearly benefit from social networks. So this will be the first app outside of Instagram that lets you into their network. That's pretty cool for us.”

And it is pretty cool for everyone involved. Hipstamatic users benefit from getting their photos viewed on the most popular photo sharing app around, while Instagram users get to see some creative images from folks using something other than Instagram itself.

It’s likely that Instagram will continue this pattern and open up its API yet further. It certainly solidifies Instagram’s place a valuable social network. Instagram CEO and co-founder, Kevin Systrom, says “I'd imagine if the experiment takes off that you'd likely see more API clients being allowed to do the same in the future.”

Instagram is valued at around $500 million, and is said to be close to raising another $40 million in funding. Though Hipstamatic may not be in that league just yet, it still generates about $10 million a year without a single round of funding.